The present invention relates to an inkjet recording method suitable for recording on every type of recording medium including a medium with no ink absorptivity.
Conventionally, water-soluble liquid ink composition has been widely used as the ink composition for inkjet recording. Besides, there has been proposed a hot-melt type inkjet recording method, using a hot-melt type ink composition made of wax or the like that remains solid at a room temperature, where the ink is liquefied by heating, emitted with the aid of some energy, and impacted on a recording medium, and then cooled immediately to harden and form a recording dot. This ink hardly causes stain during handling because it remains solid at a room temperature, and hardly causes clogging of nozzles because the ink evaporation when melted can be made minimal. In addition, the ink seldom causes blurredness because it hardens as soon as it is impacted on the medium, and so it produces an advantage that various kinds of recording media including Japanese paper, drawing paper, postcard, and plastic sheet without any pretreatment. An ink composition that provides excellent print quality irrespective of paper quality is disclosed in the U.S. Pat. Nos. 4,391,369 and 4,484,948.
An UV-setting resin type ink composition having excellent adhesion onto metallic surface is disclosed in the Japanese Application Patent Laid-Open Publication No. Sho 56-93776. Besides, there have been disclosed inkjet recording inks that are hardened by exposure to ultraviolet light: for example, the ink disclosed in the U.S. Pat. No. 4,228,438 where epoxy denaturated acrylic resin and urethane denaturated acrylic resin are used as binder and pigment in particle sizes of 5 μm or less is used as coloring material; the ink disclosed in the Japanese Application Patent Laid-Open Publication No. Sho 58-32674 (1983) where cation-polymerizing epoxy resin is used as binder; and the ink disclosed in the Japanese Application Patent Laid-Open Publication No. Hei 05-186725 (1993) where water-soluble or non-water-soluble dye is used, all of which are proposed to facilitate printing on ordinary paper and recycled paper.
As explained above, there has been desired an inkjet recording method that is capable of very fine printing, in picture quality, on various types of recording media such as plastic sheet without using special inkjet print paper.
When the above-mentioned water-soluble liquid ink is used for printing, printing on a recording medium that has no ink absorptivity is impossible and a large ink drying device is needed even if special print paper is used. Besides, it is applicable only limitedly because very fine printing is impossible due to resulting blurredness and so the resolution is limited.
While the hot-melt type ink using wax enables to print on a recording medium with no ink absorptivity and also to print at high speed, its abrasion resistance is very poor, and so the print result is lack of reliability and also less smooth.
On the other hand, since an inkjet recording method using organic pigment as coloring material has greater advantage, particularly in view of weather resistance, over an inkjet recording method using dye, wider applications are expected including not only office automation equipment, home-use printer, and office printer including facsimile but decoration on indoor and outdoor poster, large signboard, automobile, glass, elevator, wall and building, and also printing on cloth.
With a method where a recording liquid is hardened by exposure to light such as ultraviolet light, it is possible to print on a recording medium with no ink absorptivity. However, so far as an inkjet recording method that employs recording liquid which uses pigment but does not practically contain, in particular, water and organic solvent, and hardens the liquid by light such as ultraviolet light is concerned, there has never been reported of any example that is capable of very fine printing with controlled dot sizes as described in the present invention. For very fine printing, it is very important that sizes of the dots to be generated are controlled smaller. When special inkjet print paper is used, sizes of the dots to be generated can be controlled only by the amount of ink particles. In case of inkjet printing on a printing medium with no ink absorptivity, however, it is difficult to control the dot sizes only by the amount of ink particles. It is particularly difficult to control the dot sizes that comprise small particles.